Mississippi Senator’s Health Woes Narrow Republican Majority

WASHINGTON — Capitol Hill’s most anticipated arrival on Monday did not come to pass: Senator Thad Cochran, the aging Republican patrician from Mississippi, stayed at home to continue recovering from a urological issue, his aides said.

Mr. Cochran’s continued absence set off speculation about the severity of the senator’s condition, and it could have immediate ramifications for Republicans. Without his vote, Senate Republican leaders are down to a single-vote majority, 51, as they barrel toward a crucial late-week vote on a budget blueprint that would allow Congress to overhaulthe tax code.

On Monday, the chamber’s leaders were confident that they would have the votes they needed, even without Mr. Cochran, but the senator’s absence and the expectation of unified Democratic opposition will narrow an uncomfortably thin margin. At least two Republicans are thought to be uncommitted to voting for the budget plan: Senators Rand Paul of Kentucky and John McCain of Arizona, who is being treated for brain cancer but is expected to be in Washington this week.

In a statement sent to reporters on Monday morning, Brad White, Mr. Cochran’s chief of staff, said that the senator had developed a urinary tract infection as he underwent treatment for urological issues and did not offer a return date to Washington. Mr. Cochran has been absent from the Senate since late September, and his staff had previously indicated that he would return Monday.

“After a day of monitoring his condition, and on the advice of his physicians and other health care professionals, Senator Cochran has postponed his return to Washington,” Mr. White wrote. “The Senator has expressed his intention to return to the Senate when his health permits, and to fulfill his commitment and duties to the people of his state.”

An aide to Mr. Cochran, 79, said on Monday that it was not yet clear when that would be.

Mr. Cochran is the chairman of the powerful Appropriations Committee and a reliable vote for Senate leadership, making his health a source of widespread discussion in Washington, where Republicans fear he could be out of commission for the remainder of the year.

His precise condition has not been made publicly clear.

Late last month, as Senate Republicans’ most recent bid to dismantle the Affordable Care Act was collapsing, President Trump suggested on Twitter that a senator had been hospitalized and was unable to vote on the measure. It was an apparent reference to Mr. Cochran, who wrote in a tweet of his own that he had, in fact, not been hospitalized, but was recovering at home.

The absence — and the possibility that it could stretch on — is particularly concerning to Senator Mitch McConnell of Kentucky, the majority leader, who has struggled to translate Republican control in Washington into a meaningful legislative victory. Mr. McConnell’s majority was already small, and with a special Senate election scheduled for December in Alabama, it could soon become less predictable. One fewer reliable Republican vote would add to that.

In the meantime, Mr. McConnell needs to lock down the support of Mr. McCain and Mr. Paul for a budget blueprint that could come to a vote on Friday or Saturday. Mr. McCain would like to see greater increases to military spending. Mr. Paul is a fiscal hawk who has shown himself willing to buck his party’s leadership.

Fears that Mr. Cochran may not recover have also fueled conjecture about political chaos breaking out in Mississippi, a Republican stronghold that has become an open front in the battle between the party’s establishment wing and an emerging nationalist wing, backed by Stephen K. Bannon, Mr. Trump’s former chief strategist.